The present invention generally relates to an encoder, and more particularly, to an encoder provided with a plurality of detection heads.
Generally, encoders are known which offset the errors of the positional detection signals caused by the off-center rotation of the slit string of a code plate relative to the rotation center of the code plate itself by the disposition of a plurality of detection heads for one code plate, thus making possible positional detection with a high accuracy.
However, in the case in which a plurality of detection heads are provided as described hereinabove, the position of one detection head, namely, the arrangement position of the mask or the detector, must be adjusted with respect to the other detection head, so that the phase of the detection signal between the detection heads may come into conformity, and it is necessary to effect a positional setting of approximately several .mu.m in the high resolution encoder, with a problem resulting in that considerably more time is required.